public class Test {
    class Solution {
        public int[][] matrixBlockSum(int[][] mat, int k) {
            int m = mat.length;
            int n = mat[0].length;
            int[][] dp = new int[m+1][n+1];
            for(int i = 1;i <= m;i ++) {
                for(int j = 1;j <= n;j ++) {
                    dp[i][j] = dp[i-1][j] + dp[i][j-1] - dp[i-1][j-1] + mat[i-1][j-1];
                }
            }

            int[][] ret = new int[m][n];
            for(int i = 0;i < m; i ++) {
                for(int j = 0;j < n;j ++){
                    int x1 = Math.max(0,i-k)+1,y1 = Math.max(0,j-k)+1;
                    int x2 = Math.min(i+k,m-1)+1,y2 = Math.min(j+k,n-1)+1;
                    ret[i][j] = dp[x2][y2] - dp[x1-1][y2] - dp[x2][y1-1] + dp[x1-1][y1-1];
                }
            }

            return ret;
        }
    }
}
